The present invention relates to an image correcting apparatus fit for use in an imaging apparatus such as a digital still camera for processing image data compression, to an image data compressing apparatus using the image correcting apparatus and to an imaging apparatus fitted with the image correcting apparatus and the image data compressing apparatus. More particularly, the present invention relates to an image correcting apparatus for correcting conspicuous fixed image flaws and making them inconspicuous, when image data is compressed, wherein the fixed image flaws are produced in a regenerated image due to scratches on a lens, defective pixels of an imaging device and furthermore dust sticking to the surfaces of the lens and the imaging device, to an image data compressing apparatus using the image correcting apparatus and to an imaging apparatus fitted with the image correcting apparatus and the imaging data compressing apparatus.
FIG. 5 is a block diagram showing the configuration of a conventional imaging apparatus by way of example. The exemplary imaging apparatus 60 in FIG. 5 essentially comprises a lens 62, an imaging device 64, an image processing circuit 66, a compression circuit 68 and a frame memory 70. An image formed through the lens 62 and inputted into the imaging device 64 such as CCD is converted into an image signal when subjected by the imaging device 64 to photoelectric conversion, converted by the image processing circuit 66 into a format of such as RGB, which is divided into image data on a block basis, encoded and compressed by the compression circuit 68 and stored in the frame memory 70 after the data quantity is reduced.
As the information volume of image data is generally large, data compressing techniques for reducing the information volume by compressing the image data are employed for such imaging apparatus as digital still cameras when the image data is transferred to personal computers or preserved in external storage units. There is a JPEG (Joint Photographic Experts Group) algorithm, for example, which is an international standard encoding system for still color images as one of the aforementioned techniques.
In the JPEG algorithm, encoding image data is sequentially carried out by, for example, dividing the image data into blocks of horizontal 8 pixels.times.vertical 8 pixels with a block as one unit. As shown in FIG. 6, in the compression circuit 68, each image data in each block is converted into coefficients of frequency components by an orthogonal transformation circuit 72, quantized by a quantization circuit 74 using a quantization table 73 and subjected by a variable-length encoding circuit 76 to variable-length encoding in order to make the image data a compressed data.
In the case of the aforesaid imaging apparatus 60, fixed image flaws such as white points or black points are produced in a regenerated image due to, for example, scratches on the lens 62, defective pixels of the imaging device 64 and furthermore dust sticking to the surfaces of the lens 62 and the imaging device 64. In order to deal with the fixed image flaws, there have heretofore been followed the steps of making an inspection when products are forwarded, replacing the lens 62 and the imaging device 64 whenever the product has not met predetermined standards and carrying out reassembly of the parts when dust is involved. In consequence, there have developed problems in that a yield rate is lowered and that the products tend to become costly.
An image flaw correcting method for correcting defective pixels of an imaging device as one of the means for solving the problems above described has heretofore been proposed in, for example, Japanese Patent Laid-Open Publication No. 6-105241/1994. This image flaw correcting method is intended to calculate a matrix of constants and a matrix of coefficients of equations corresponding to discrete cosine transformation based on the defective pixels of the imaging device, calculate a solution of the equations from an inverse matrix of these matrix of constants and matrix of coefficients, and correct the defective pixels based on this solution.
Furthermore, this image flaw correcting method is said to be able to put CCDs which are more defective than before into practice, and to realize an inexpensive camera system in this result. However, this image flaw correcting method is aimed to correct image data relevant to defective pixels of the imaging device and the problem is that it is incapable of dealing with image flaws of the regenerated image due to scratches on the lens and dust sticking to the surfaces of the lens and the imaging device.